1. Field of the Invention
The present invention relates to movable X-ray sources for delivering to an object of interest a conditioned, monochromatic, high intensity X-ray beam.
2. Background Art
Conventional X-ray sources exist that deliver low energy (usually less than 150 keV) X-ray radiation (hereinafter xe2x80x9cX-raysxe2x80x9d, xe2x80x9cX-ray beamsxe2x80x9d, or xe2x80x9cX-ray radiationxe2x80x9d) to an object or target. Such conventional sources are exemplified by a sealed X-ray tube and an X-ray tube with a rotating anode. There are also X-ray sources containing X-ray tubes which are attached to conditioning (e.g., collimating or focusing) optics. However, such conventional approaches leave unsolved the challenge of delivering a conditioned, monochromatic beam with a high intensity.
To bring high intensity X-ray radiation to a relatively small object by a narrow focusing or collimating beam or by a beam with a limited angular aperture, conventional X-ray sources have certain disadvantages:
1. Low efficiency (about 0.2%), i.e., the ratio of output energy emitted as X-rays to the input energy associated with incident electrons; and
2. Unfavorable spatial distribution. In an X-ray tube, the spatial distribution of X-rays emitted from a thick anode is spherical. For an angular aperture (for example, less than 0.6xc3x970.6 degrees), only a small fraction of the emitted X-rays can be used.
An example of systems having an angular aperture of 0.6xc3x970.6 degrees is Gutman Optics, available from Osmic, Inc. of Troy, Mich. Such a system is described in a product brochure entitled xe2x80x9cGutman Optics,xe2x80x9d which is incorporated by reference herein.
Various X-ray sources are used in several applications. X-ray tubes with an energy below 150 keV emit radiation that is distributed omnidirectionally with a polychromatic spectrum and narrow characteristic lines. Such tubes are often used in the industrial environment, e.g. in analytical instrumentation, non-destructive testing, and for similar applications. These X-ray sources are typified by a low intensity of the generated X-ray beam. Megavoltage X-ray tubes with a transmitting-type target, (so-called linear accelerators) emit a directed high intensity polychromatic beam. Linear accelerators are used in X-ray security/inspection systems and in medical applications, such as radiation therapy. Their effectiveness, however, is limited because the highest intensity of the directed polychromatic X-ray radiation is delivered by the high energy (more than 1 MeV) part of the spectrum with high penetration that, in turn, can damage healthy tissue. Additionally, such radiation sources require heavy shielding systems and large power supplies. These requirements, in turn, mandate separate facilities for their accommodation.
By combining a linear accelerator having a thin anode and an electron trap and conditioning optics, the disclosed invention creates and delivers a high intensity monochromatic X-ray beam in a region of energy comparable to X-ray tubes and with an intensity comparable to that of a conventional linear accelerator. The electron trap contains a strong magnet for deflecting a high energy electron beam that penetrates a thin anode. The invention also provides a cell with a material that absorbs high energy electrons and ensures separation between the emergent X- rays and electron beams.
Due to the thin anode, high energy X-ray scattering, especially in a direction divergent from the optical axis, is decreased by several orders of magnitude. This simplifies the provision of a shielding system, while creating a movable high intensity X-ray source. In medical applications, for example, such a type of X-ray source can be used in the operating room while significantly decreasing the cost of treatment.
It is an object of the present invention to provide a moveable X-ray source that has an X-ray linear accelerator with a thin anode and conditioning optics for delivery to an object of a high intensity, monochromatic X-ray beam having a selectable shape and wavelength.
It is a further object of the invention to provide an electron trap for separating a high energy electron beam transmitted through an anode from an X-ray beam that emerges from the anode, while absorbing the electron beam to prevent high energy X-ray scattering.
It is still further an object of the invention to provide an optical housing constructed from a thick, heavy metal (such as lead or tantalum) that serves as a barrier to penetration by high energy X-rays.
It is still another object of the invention to provide with the above-mentioned optics, a stop diaphragm in the form of a thick, heavy metal diaphragm that prevents direct elimination of the object by any X-ray radiation, including high energy X-ray radiation.
It is yet further an object of the invention to provide slits and a stop diaphragm such that the inner surfaces of the slits and the outer surface of the diaphragm remain parallel to the edge of the X-ray beam.
Additionally, it is an object of the invention to provide a method and system that does not require a vacuum in which to operate.
Additionally, it is an object of the invention to provide a method and system which does not depend primarily on the material of the target used.